Messages in this thread | | | Date | Mon, 28 Mar 2022 17:56:07 +0200 | From | Peter Zijlstra <> | Subject | Re: [External] Re: [PATCH] sched/fair: fix broken bandwidth control with nohz_full |
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On Mon, Mar 28, 2022 at 11:40:25PM +0800, Chengming Zhou wrote:
> > NOHZ_FULL is for use-cases that 'never' intend to go into the kernel, > > your use-case actively relies on going into the kernel. Hence the > > confusion. > > In fact, I put a testcase at the end of git message, in which only run > a userspace loop workload: > > cd /sys/fs/cgroup > echo "+cpu" > cgroup.subtree_control > > mkdir test > echo "105000 100000" > test/cpu.max > > echo $$ > test/cgroup.procs > taskset -c 1 bash -c "while true; do let i++; done" --> will be throttled
Ofcourse.. I'm arguing that bandiwdth control and NOHZ_FULL are somewhat mutually exclusive, use-case wise. So I really don't get why you'd want them both.
NOHZ_FULL says, "I 'never' intend to go to the kernel"
bandwidth control says: "I expect to be sharing the system and must be interrupted to not consume too much time", which very much implies: "I will go into the kernel".
The trade-off we make to make NOHZ_FULL work, makes system enter/exit *far* more expensive. There's also people asking to outright kill a task that causes entry under NOHZ_FULL.
So yes, you can configure it, but why does it make sense?
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